A typical molten metal facility includes a furnace with a pump for moving molten metal. This invention provides a centrifugal impeller pump that will move more molten metal with a minimum of submergence while retaining a very high overall efficiency. This goal is achieved by accelerating flow into the impeller pump by utilizing the full available pressure head of metal above the pump.
An optimum head is acquired by making my pump very shallow and locating it on the bottom of the well.
A problem with a conventional pump having an excessive height is a tendency to suck dross into the pump, which is undesirable. To compensate, the pump inlet speed is reduced. Reducing the available inlet velocity reduces the pump flow capacity.
In my design, the impeller that moves the metal has a top plate with a radial inlet opening that serves as an inducer. The molten metal passes through the impeller inducer top plate to a horizontal impeller inducer outlet and then into the collector volute in the pump base. The impeller pump achieves three times the molten metal flow rate, without increasing the motor size three times. The reason is that a dual inducer generates higher outlet impeller tip velocity, thus generating higher pressures and flows, consequentially increasing both the mechanical and volumetric efficiencies of the pump.
The top plate of the pump has several inlet inducer openings, typically five to seven, which scoop the molten metal into the rotating pump. Each impeller top plate inlet passage has a chamfered entrance or inducer facing the approaching metal. The chamfered leading edge sucks the molten metal axially down, and the chamfered trailing edge further accelerates the metal downwardly increasing the metal flow velocity.
The reason for the high efficiency of these special, chamfered inducers is that metal flow is a function of both the available inlet head velocity, and the inlet inducer shape. The impeller inlet of my pump has a trapezoidal shape that maximizes the inlet area within the pump impeller available area. The inlet inducer angle matches the rotational velocity and flow axial velocity.
The high recirculation and gas injection efficiency of the metal flow is achieved by making the pump exit velocity as high as necessary to efficiently discharge the metal so as to penetrate the metal pool outside the pump.
The impeller contains an exit inducer as well. Using two inducers is also novel. The impeller exit inducer controls the metal flow exit angle, from the impeller, and the metal flow speed, allowing the designer to vary the pump flow versus pressure characteristics, and to select an optimum volute configuration for the particular application under consideration.
The preferred embodiment of the invention will pump at 300 rpm, 2500 gallons per minute of molten metal out of a pump having a seven and a half-inch tall base. It is so effective that when the pump operates at least 300 rpm, the molten metal shows a charge well penetration of up to 18 feet with overall efficiencies well over 60% with a pump flow capacity of 2400 to 2800 gpm in a pump base of 30″×36″×7.5″ in height.
A dual suction impeller pump is also disclosed for delivering 4800/5000 gallons per minute at 300 rpm with a pump base foot print of 30″×36″ and only 10.5″ in height.
Prior art related to this technology is disclosed in U.S. Pat. No. 3,244,109 issued Apr. 5, 1966 to U. M. W. Barske for “Centrifugal Pumps” and U.S. Pat. No. 4,786,230 issued Nov. 22, 1988 to Bruno H. Thut for “Dual Volute Molten Metal Pump and Selective Outlet Discriminating Means”.
Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description.